Do I need a throwaway flight to apply for a 60-day SETV to Thailand?

You need to check consulate in Sydney about their detailed requirement for SETV. That’s consulate specific if you need to provide outbound tickets or not and what type of yes.

They asked for a onward flight. So I bought a flight to Vietnam $50.

I think the airlines are a bit more flexible when you have a visa rather than travelling with a waiver , my wife and I applied for a setv and only showed the flight in and 1 weeks hotel stay and they were approved in 5 days (uk) I did contact emirates about the one way and explained that we didn’t know what country we would be flying home from as we are spending 6 months travelling Asia with no set itinerary, they said just to show the visa at check in

Update , just checked in all that was asked was how long in Bangkok , just said we’re travelling around and going to Cambodia at some point and that was it , Glasgow airport emirates

I arrived yesterday on Cathay Pacific. In NYC they asked for a departing flight. I told them I didn’t have one as I was leaving by a land border to Laos after going to Chiang Mai. She asked me for the dates and let

It go. I was prepared to buy a departing flight on points if necessary then cancel immediately with

No cost to me.

You can search the internet forever and never find the definitive answer to this question. All I can say is others have said, it'll be your airline who will enforce this rule, so check with them

What embassy are you applying at? Some embassies want to see an onward ticket, but I think you could upload a note stating your intention of applying for a non O in country to satisfy the embassy. Satisfying the airline on the other hand is a different matter.

You need to ask your airline

It's your airline that may ask to see PROOF of your departing within the number of days you are going to be stamped in on arrival into Thailand.